Composite bearings having a polyimide matrix

ABSTRACT

The present disclosure relates to bearing and seal assemblies comprising a composite structure which includes a substrate and a layer disposed on the substrate. The layer disposed on the substrate includes a polyimide matrix and a filler dispersed within the polyimide matrix. The filler can be a thermoplastic polymer, such as PTFE, and/or an organic filler. The bearing assembly can exhibit a synergistic improvement in wear resistance and coefficient of friction.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority under 35 U.S.C. §119(e) to U.S.Provisional Patent Application No. 61/922,421 entitled, “COMPOSITEBEARINGS HAVING A POLYIMIDE MATRIX,” by Nafih Mekhilef et al., filedDec. 31, 2013. Each patent application cited herein is herebyincorporated by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to composites, and more particularly to,composites used to construct bearings and seals.

RELATED ART

Bearing and seal assemblies are widely used in the industry as ininterface between a movable surface and a stationary surface.Traditionally, it is desired to increase the wear resistance of thebearing assembly while also having a desirably low coefficient offriction. However, most attempts to improve the wear resistancenegatively affect the coefficient of friction and vice versa.Accordingly, a need exist to develop novel bearing and seal assembliesin which the composite exhibits both an improved wear resistance andimproved coefficient of friction.

Moreover, the method of producing composite bearings, and particularlycomposite bearings incorporating a polyimide matrix have drawbacks. Inparticular, an in-situ or continuous method of forming the polyimidematrix is desired. Such in-situ imidization and formation of polyimidematrixes with dispersed fillers or thermoplastics in composites,bearings and seals has not been disclosed or suggested.

The present disclosure provides a composite assembly satisfying theseand other needs as will be illustrated in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example and are not limited in theaccompanying figures.

FIG. 1 includes an illustration of a composite according to anembodiment of the disclosure.

FIG. 2 includes an illustration of a composite according to anotherembodiment of the disclosure.

FIG. 3 includes an illustration of a testing assembly for wear rates andcoefficient of frictions according to ASTM G-77.

FIG. 4 illustrates a record of the wear and temperature as a function oftime for Sample 1.

FIG. 5 illustrates a record of the coefficient of friction as a functionof time for Sample 1.

FIG. 6 illustrates a record of the wear and temperature as a function oftime for Sample 2.

FIG. 7 illustrates a record of the coefficient of friction as a functionof time for Sample 2.

FIG. 8 illustrates a record of the wear and temperature as a function oftime for Sample 3.

FIG. 9 illustrates a record of the coefficient of friction as a functionof time for Sample 3.

FIGS. 10 and 11 illustrate the SEM of Sample 1.

FIGS. 12 and 13 illustrate the SEM of Sample 2.

FIGS. 14 and 15 illustrate the SEM of Sample 3.

FIG. 16 illustrates the dry coefficient of friction data for example 3.

FIG. 17 illustrates the lubricated coefficient of friction data forexample 3.

FIG. 18 illustrates a bearing pre-composite according to one embodiment.

FIG. 19 illustrates a bearing pre-composite according to anotherembodiment.

FIG. 20 illustrates the bearing pre-composite of FIG. 19 with therelease layer removed according to one embodiment.

Skilled artisans appreciate that elements in the figures are illustratedfor simplicity and clarity and have not necessarily been drawn to scale.For example, the dimensions of some of the elements in the figures maybe exaggerated relative to other elements to help to improveunderstanding of embodiments of the invention.

DETAILED DESCRIPTION

The following description in combination with the figures is provided toassist in understanding the teachings disclosed herein. The followingdiscussion will focus on specific implementations and embodiments of theteachings. This focus is provided to assist in describing the teachingsand should not be interpreted as a limitation on the scope orapplicability of the teachings. However, other embodiments can be usedbased on the teachings as disclosed in this application.

The terms “comprises,” “comprising,” “includes,” “including,” “has,”“having” or any other variation thereof, are intended to cover anon-exclusive inclusion. For example, a method, article, or apparatusthat comprises a list of features is not necessarily limited only tothose features but may include other features not expressly listed orinherent to such method, article, or apparatus. Further, unlessexpressly stated to the contrary, “or” refers to an inclusive-or and notto an exclusive-or. For example, a condition A or B is satisfied by anyone of the following: A is true (or present) and B is false (or notpresent), A is false (or not present) and B is true (or present), andboth A and B are true (or present).

Also, the use of “a” or “an” is employed to describe elements andcomponents described herein. This is done merely for convenience and togive a general sense of the scope of the invention. This descriptionshould be read to include one, at least one, or the singular as alsoincluding the plural, or vice versa, unless it is clear that it is meantotherwise. For example, when a single item is described herein, morethan one item may be used in place of a single item. Similarly, wheremore than one item is described herein, a single item may be substitutedfor that more than one item.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. The materials, methods, andexamples are illustrative only and not intended to be limiting. To theextent not described herein, many details regarding specific materialsand processing acts are conventional and may be found in textbooks andother sources within the composites, bearings and seals arts.

The following disclosure describes composites, and particularlycomposite bearings having a polyimide matrix filled with materials, suchas a thermoplastic, dispersed within the polyimide matrix. Alsodescribed is a method of forming a composite, wherein a mixturecontaining a polyimide precursor or imide monomers is deposited on asubstrate and imidized on the substrate. Such in-situ imidization andformation of polyimide matrixes with dispersed fillers or thermoplasticsin composites, bearings and seals has not been disclosed or suggested.The concepts are better understood in view of the embodiments describedbelow that illustrate and do not limit the scope of the presentinvention

FIG. 1 illustrates a composite 100 containing a substrate 20 and a firstlayer 30 disposed on the substrate 20. As illustrated, the first layer30 may be disposed directly adjacent the substrate 20 such that thefirst layer 30 is directly contacting the substrate 20. However, asdiscussed in more detail below, the composite may include intermediatelayer(s) disposed between the substrate and first layer 30.

The substrate 20 can be constructed out of any material capable of beingformed into a bearing or seal. In certain embodiments, the substrate cancontain a metal, such as steel, aluminum, bronze, copper, orcombinations thereof.

The surface 22 of the substrate 20 adjacent to first layer 30 may bemechanically treated to improve adhesion between the substrate and firstlayer 30. For example, mechanically treating the surface 22 of thesubstrate 20 can include blasting or mechanically etching the surface 22of the substrate 20. The surface 22 of the substrate 20 can bemechanically treated such that the surface 22 of the substrate 20 has anadvantageous surface roughness.

Referring again to FIG. 1, adjacent the substrate 20 may be a firstlayer 30. The first layer 30 can be formed of a combination ofmaterials. In particular embodiments, the first layer 30 can contain apolyimide matrix and a filler dispersed within the polyimide matrix.

As used herein, “polyimide matrix” refers to a crosslinked network ofpolyimide, where the polyimide is at least about 25 wt. % of the firstlayer, based on the total weight of the first layer 30.

As will be discussed in more detail below, the polyimide matrix can beformed from imidizing a polyimide precursor after deposition on asubstrate. A suitable polyimide precursor can include, for example,poly(amic) acid (PAA). The poly(amic) acid (PAA) can be a reactionproduct of a monomer mixture containing at least two different monomers.In certain embodiments, the at least two different monomers can selectedfrom the group consisting of: pyromellitic dianhydride (PMDA), 3,3′-4,4′-biphenyltetracarboxylic dianhydride (BPDA), 2, 2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA), 2, 2′-bis[4-(3, 4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA),benzophenonetetracarboxylic dianhydride (BTDA), and 4, 4′-oxydianiline(ODA), or m-phenylene diamine (m-PDA), 4, 4′-diaminophenyl sulphone(4,4′-DDS), p-phenylene diamine (p-PDA), and methylene dianiline (MDA).As such, in particular embodiments, the polyimide matrix can be acrosslinked, reaction product of at least two different monomers listedabove. In particular embodiments the polyimide matrix may be a purepolyimide matrix. As used herein, the phrase pure polyimide matrix is apolyimide matrix that is essentially free of copolymers with imidemonomers. In other words, in certain embodiments, the polyimide matrixcan be essentially free of non-imide monomers.

Further, in certain embodiments, the polyamic acid can be derived from afirst monomer and a second monomer. The first monomer can be selectedfrom the group consisting of pyromellitic dianhydride (PMDA), 3,3′-4,4′-biphenyltetracarboxylic dianhydride (BPDA), 2, 2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA), 2, 2′-bis[4-(3, 4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA),benzophenonetetracarboxylic dianhydride (BTDA), and any combinationthereof. The second monomer can be selected from the group consisting of4, 4′-oxydianiline (ODA), or m-phenylene diamine (m-PDA), 4,4′-diaminophenyl sulphone (4,4′-DDS), p-phenylene diamine (p-PDA),methylene dianiline (MDA), and any combination thereof.

In particular embodiments, the polyimide matrix can be derived from apolyamic acid salt. For example, polyamic acid can be dissolved in asolvent such as N-methylpyrolidone and reacted with, for example, atertiary amine, to form a water soluble polyamic acid salt solution. Thepolyamic acid salt solution can then be blended with an aqueousdispersion of the filler, and because the polyamic acid salt solution ismiscible in water, a more uniform dispersion of the filler within thepolyimide matrix can be produced. After application to a substrate andcuring, volatile materials present in the first layer, including thesalt moiety of the polyamic acid salt as the imide bonds are formedduring curing.

As discussed above, first layer 30 may also contain a filler dispersedwithin the polyimide matrix. Fillers can include, but are not limitedto, carbon graphite, grapheme, carbon nanotubes, ekonol, glass fibers, apolymeric compound such as a thermoplastic, an organic compound,inorganic compound, or combinations thereof.

In particular embodiments, the filler can be a thermoplastic material.In certain embodiments, the thermoplastic can be a fluoropolymer, forexample a perfluoropolymer. In even more particular embodiments, thethermoplastic can be PTFE, PVF, PVDF, PCTFE, PFA, FEP, ETFE, orcombinations thereof. In very particular embodiments, the thermoplasticcan include PTFE or even consist essentially of PTFE. Further, thethermoplastic, such as PTFE, can be a regrind thermoplastic.

In other particular embodiments, the filler can be an organic filler.For example, in certain embodiments, the organic filler can comprise anaromatic polyester, a recycled polyimide, polyamide ether imide,polyamide imide, PEEK, PEEK-like polymers of polyaryl family, liquidcrystalline polymers (LCP), polybenzimidazole, or combinations thereof.

The filler can be present in the mixture in an amount of from greaterthan 0 wt. % to 80 wt. % by weight, based on the combined weight of thethermoplastic, polyimide precursor, and filler. For example, inparticular embodiments, the filler can be present in the mixture in anamount of at least 1 wt. %, at least 3 wt. %, at least 5 wt. %, at least7 wt. %, at least 8 wt. %, at least 10 wt. %, at least 12 wt. %, atleast 14 wt. %, at least 16 wt. %, at least 18 wt. %, at least 20 wt. %,at least 22 wt. %, at least 24 wt. %, at least 26 wt. %, at least 28 wt.%, or even at least 30 wt. % based on the combined weight of thethermoplastic, polyimide precursor, and filler. Further, in particularembodiments, the filler can be present in the mixture in an amount of nogreater than 80 wt. %, no greater than 78 wt. %, no greater than 76 wt.%, no greater than 74 wt. %, no greater than 72 wt. %, no greater than70 wt. %, no greater than 68 wt. %, no greater than 66 wt. %, no greaterthan 64 wt. %, no greater than 62 wt. %, or even no greater than 60 wt.% based on the combined weight of the thermoplastic, polyimideprecursor, and filler. Moreover, in particular embodiments, the fillercan be present in the mixture in a range of any of the minimum andmaximums provided above, such as in a range of 1 wt. % to 80 wt. %, oreven 10 wt. % to 70 wt. % based on the combined weight of thethermoplastic, polyimide precursor, and filler.

It is to be understood the mixture can include any combination of thefillers provided above. In particular embodiments, the mixture caninclude a thermoplastic filler and an organic filler.

First layer 30 may also contain any desired additive. For example, someadditives may include a thickener or stabilizer. For example,stabilizers may include surfactants such as perfluoroalkoxy compounds,viscosifiers. Thickeners can include, for example, algocel and glycolsor combinations thereof. The additives may be added in any desiredamount to induce their desired additive effect.

In particular embodiments, first layer 30 can have a thickness of nogreater than about 1 mm, no greater than about 800 microns, no greaterthan about 500 microns, no greater than about 300 microns, no greaterthan about 250 microns, no greater than about 200 microns, or even nogreater than about 175 microns. Further, in certain embodiments, firstlayer 30 can have a thickness of at least about 0.01 microns, at leastabout 1 micron, at least about 50 microns, or even at least about 100microns. It is to be understood that first layer 30 can contain onelayer or more than one layer. In particular embodiments, first layer 30can contain more than one layer that is formed from multiple passesthrough a coating operation.

First layer 30 can have a certain porosity. For example, in certainembodiments, first layer 30 can have a porosity of at least about 0.01%,at least about 0.05%, or even at least about 0.1%.

In certain embodiments, as particularly illustrated in FIG. 2, one ormore additional intermediate layers 40 may be disposed between thesubstrate 20 and the first layer 30. An intermediate layer 40 may beprovided to, for example, improve adhesion between the first layer 30and the substrate 20. As can be appreciated by one of skill in the art,the particular choice of intermediate layer 40 will depend on thesubstrate 20 and composition of first layer 30. In particularembodiments, the intermediate layer 40 may contain zinc or a zinccontaining compound. The additional intermediate layer may be providedas an alternative to or in addition to the mechanical treating of thesurface 22 of the substrate 20 described above.

A particular advantage of the present disclosure is the achievement ofcertain performance properties such as average coefficient of friction,average wear resistance, and the ability to pass the Laminator AdhesionTest (Erichsen). It has heretofore not been known how to achieve theperformance characteristics, and particularly combinations ofperformance characteristics described herein.

One characteristic that quantifies a bearing's performance can be itsaverage coefficient of friction (COF). The average coefficient offriction (COF) is an industry standard term and can be measuredaccording to ASTM G-77.

In certain embodiments, a bearing according to the disclosure herein canhave an average coefficient of friction (COF) of no greater than about1, no greater than about 0.8, no greater than about 0.7, no greater thanabout 0.6, no greater than about 0.5, no greater than about 0.4, nogreater than about 0.3, no greater than about 0.25, no greater thanabout 0.2, no greater than about 0.18, no greater than about 0.15, oreven no greater than about 0.12 as measured according to ASTM G-77.Further, in certain embodiments, a bearing according to the disclosureherein can have an average coefficient of friction (COF) of no less thanabout 0.001, no less than about 0.01, or even no less than about 0.05 asmeasured according to ASTM G-77. Moreover, in particular embodiments, abearing according to the disclosure herein can have an averagecoefficient of friction within a range of any of the minimum andmaximums provided above, such as in a range of 0.001 to 1, or even from0.01 to 0.7.

Another characteristic that can quantify a bearing's performance is itsaverage wear resistance. The wear resistance is a measurement of theamount of material that is removed from the bearing during a wear testconducted according to ASTM G-77.

In certain embodiments, a bearing according to the disclosure herein canhave an average wear resistance of no greater than about 10 mm³, nogreater than about 8 mm³, no greater than 5 mm³, no greater than about 4mm³, no greater than about 3 mm³, no greater than about 2.9 mm³, nogreater than about 2 mm³, no greater than about 1.5 mm³, no greater thanabout 1.3 mm³, no greater than about 1.1 mm³, no greater than about 1mm³, no greater than about 0.8 mm³, no greater than about 0.6 mm³, nogreater than about 0.5 mm³, no greater than about 0.3 mm³, or even nogreater than about 0 2 mm³ as measured according to ASTM G-77. Further,in certain embodiments, a bearing according to the disclosure herein canhave an average wear resistance of no less than about 0.001 mm³, no lessthan about 0.01 mm³, or even no less than about 0.05 mm³ as measuredaccording to ASTM G-77. Moreover, in particular embodiments, a bearingaccording to the disclosure herein can have an average wear resistancein a range of any of the minimum and maximum values provided above, suchas in a range of 0.001 mm³ to 10 mm³, or even from 0.01 mm³ to 4 mm³.

A third characteristic which can quantify a bearing's performance is theability of the bearing to pass the Laminator Adhesion Test (Erichsen).The Laminator Adhesion Test is a measure of the adherence of the firstlayer to the second layer in the bearing assembly and is well known inthe art.

In certain embodiments, a bearing according to the disclosure herein canpass the Laminator Adhesion Test (Erichsen).

According to another aspect of the disclosure, methods for forming acomposite sheet and forming a composite bearing are described. In oneembodiment, the method can include: providing a polyimide precursor orimide monomers; providing a filler; providing a solvent; blending thefiller, a solvent, and the polyimide precursor or imide monomers to forma mixture; depositing the mixture on a substrate; and thermally curingthe substrate and deposited mixture. To form a composite bearing, themethod may further include forming a composite bearing from thecomposite sheet.

In certain embodiments, the formation of the composite may be acontinuous process. For example, the imidization can be performedin-situ such that the mixture with a polyimide precursor or monomers andfiller can be mixed and applied to the substrate, and then imidizedin-situ after depositing on the substrate.

The method may form a bearing having a coefficient of friction and awear resistance as described above. For example, in particularembodiments, the method may form a bearing having a coefficient offriction of less than about 1, and a wear resistance of less than 2.9mm³.

The polyimide precursor can contain uncrosslinked polyimide or imidemonomers. For example, the polyimide precursor can contain a poly(amic)acid. The poly(amic) acid can be derived from the reaction of at leasttwo different monomers. In particular embodiments, the at least twodifferent monomers selected from the group consisting of: pyromelliticdianhydride (PMDA), 3,3′-4, 4′-biphenyltetracarboxylic dianhydride(BPDA), 2, 2-bis (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride(6FDA), 2, 2′-bis [4-(3, 4-dicarboxyphenoxy)phenyl]propane dianhydride(BPADA), benzophenonetetracarboxylic dianhydride (BTDA), and 4,4′-oxydianiline (ODA), or m-phenylene diamine (m-PDA), 4,4′-diaminophenyl sulphone (4,4′-DDS), p-phenylene diamine (p-PDA), andmethylene dianiline (MDA).

In even further particular embodiments, the first monomer can contain amonomer selected from the group consisting of pyromellitic dianhydride(PMDA), 3,3′-4, 4′-biphenyltetracarboxylic dianhydride (BPDA), 2, 2-bis(3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA), 2, 2′-bis[4-(3, 4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA),benzophenonetetracarboxylic dianhydride (BTDA), and any combinationthereof; and the second monomer can contain a monomer selected from thegroup consisting of 4, 4′-oxydianiline (ODA), or m-phenylene diamine(m-PDA), 4, 4′-diaminophenyl sulphone (4,4′-DDS), p-phenylene diamine(p-PDA), methylene dianiline (MDA), and any combination thereof.

In particular embodiments, the poly(amic) acid can be in the form of asalt as described in detail above. Accordingly, in particularembodiments, the method can include providing, or even forming, apoly(amic) acid salt. For example, in certain embodiments, polyamic acidcan be combined in a solvent and reacted with, for example, a tertiaryamine to form a water soluble polyamic acid salt mixture. An aqueousdispersion containing the filler can then be added to the polyamic acidsalt mixture and since the polyamic acid salt mixture is water soluble,the filler can be evenly dispersed throughout the polyamic acid salt andmaintain their even dispersion after imidization during curing.

In particular embodiments, the polyimide precursor can be present in themixture in an amount of from 20 to 99% by weight, based on the combinedweight of the thermoplastic and the polyimide precursor. For example, incertain embodiments, the polyimide precursor can be present in themixture in an amount of at least 20 wt. %, at least 22 wt. %, at least24 wt. %, at least 26 wt. %, at least 28 wt. %, at least 30 wt. %, atleast 32 wt. %, at least 34 wt. %, at least 36 wt. %, at least 38 wt. %,at least 40 wt. %, based on the combined weight of the thermoplastic andthe polyimide precursor. Further, in certain embodiments, the polyimideprecursor can be present in the mixture in an amount of no greater than99 wt. %, no greater than 97 wt. %, no greater than 95 wt. %, no greaterthan 93 wt. %, no greater than 91 wt. %, no greater than 99 wt. %, nogreater than 99 wt. %, no greater than 99 wt. %, no greater than 99 wt.%, no greater than 99 wt. %, based on the combined weight of the fillerand the polyimide precursor.

As discussed above, the method can include providing a filler andincorporating the filler into the mixture and held within the polyimidematrix upon imidization and curing.

As discussed above, the filler can be a number of different materials,and in particular embodiments can include a thermoplastic, an organicfiller, others, or combinations thereof. In certain embodiments, when acombination of fillers is used, such as a thermoplastic and/or organicfillers, the fillers can be combined together before being combined withthe other components.

In particular embodiments, before being mixed into the solvent, thefiller can be in particulate form. In such embodiments, the filler, andparticularly a thermoplastic filler, and even more particularly PTFE,can have an average particle size (D₅₀) of at least about 1 micron, atleast about 3 microns, at least about 5 microns, at least about 10microns, at least about 15 microns, or even at least about 20 microns.Moreover, in certain embodiments, the filler can have an averageparticle size (D₅₀) of no greater than about 1000 microns, no greaterthan about 500 microns, no greater than about 50 microns, no greaterthan about 30 microns, no greater than about 20 microns, or even nogreater than about 10 microns. Furthermore, the filler can have anaverage particle size (D₅₀) in a range between any of the maximum andminimum values described herein, such as in a range of from about 1micron to 50 microns, from about 3 microns to about 30 microns, or evenfrom about 5 microns to about 20 microns.

Further, the filler, before being combined with the polyimide precursoror imide monomers can be, for example, in a powdered form, or in otherembodiments, in a dispersed phase in a solvent, such as water. Infurther embodiments, the mixture can be formed with both powdered fillerand filler dispersed in a solvent.

In certain embodiments, the filler, such as a thermoplastic filler, canbe present in the mixture in an amount of from greater than 0 to 80% byweight, based on the combined weight of the filler and the polyimideprecursor. For example, in particular embodiments, the filler can bepresent in the mixture in an amount of at least 1 wt. %, at least 3 wt.%, at least 5 wt. %, at least 7 wt. %, at least 8 wt. %, at least 10 wt.%, at least 12 wt. %, at least 14 wt. %, at least 16 wt. %, at least 18wt. %, at least 20 wt. %, at least 22 wt. %, at least 24 wt. %, at least26 wt. %, at least 28 wt. %, or even at least 30 wt. % based on thecombined weight of the filler and the polyimide precursor. Further, inparticular embodiments, the filler can be present in the mixture in anamount of no greater than 80 wt. %, no greater than 78 wt. %, no greaterthan 76 wt. %, no greater than 74 wt. %, no greater than 72 wt. %, nogreater than 70 wt. %, no greater than 68 wt. %, no greater than 66 wt.%, no greater than 64 wt. %, no greater than 62 wt. %, or even nogreater than 60 wt. % based on the combined weight of the filler and thepolyimide precursor. Moreover, in particular embodiments, the filler canbe present in the mixture in a range of any of the minimum and maximumsprovided above, such as in a range of 1 wt. % to 80 wt. %, or even 10wt. % to 70 wt. % based on the combined weight of the filler and thepolyimide precursor.

In certain embodiments, a solvent can be provided with the filler,polyimide precursor or imide monomers, or can be added to the componentsindividually or after combining the filler and polyimide precursor orimide monomers. In certain embodiments, the solvent can be mixed withthe filler before mixing with the polyimide precursor or imide monomers.Further, a solvent can be added to the mixture. In particularembodiments, the solvent can include N-methyl-pyrrolidone (NMP),dimethylformamide, dimethylacetamide, diglyme, dimethylsulfoxide,xylene, or any combination thereof.

In particular embodiments, the solvent can include an aqueous component.In very particular embodiments, the solvent can include, at least, waterand NMP.

As discussed above, the method may include blending the polyimideprecursor or imide monomers, filler and optional solvent to form amixture.

In certain embodiments, the components may be blended for a period oftime of at least about 1 minute, at least about 5 minutes, or even atleast about 15 minutes.

As discussed above, the method may include depositing the mixture on asubstrate. The substrate can be any material discussed above, inparticular, a metal such as steel, aluminum, bronze, copper, orcombinations thereof.

The mixture may be deposited on the substrate by any suitable method.For example, in particular embodiments, the mixture can be deposited onthe substrate by dip coating, spray coating, knife coating, or any otheruseful method. In particular embodiments, the mixture can be depositedon the substrate by dip coating. It is to be appreciated that firstlayer 30 can contain more than one layer, such as, being formed frommultiple passes through the deposition operation. The mixture can bethermally cured between layers.

A particular advantage of certain embodiments of the present disclosureis the ability to form first layer 30 by a coating operation instead of,form example, skiving or extruding. Traditional sliding layers formedfrom coating operations have not been able to achieve the performancecharacteristics described herein. Moreover, by using a coatingoperation, the filler materials, such as thermoplastic material, canmaintain their morphology unlike extrusion or skiving operations, whichaffect the filler morphology.

The mixture may be deposited such that the first layer 30 has a desiredthickness. For example, the thickness of first layer 30 can be anythickness described above. Moreover, in certain embodiments, the methodmay further include adjusting the viscosity of the mixture to obtain adesired thickness of the mixture when coated on the substrate. Forexample, in some embodiments, the viscosity of the mixture may beadjusted as desired by varying the percentage of the components and/oraddition of a viscosity modifying agent.

After deposition of the first layer, the method may include thermallycuring the deposited mixture of polyimide precursor or imide monomers,thermoplastic, and solvent. Thermally curing results in the formation ofpolyimide (in the case of using imide monomers) and cross linking of thepolyimide precursor while driving off the solvent. In certainembodiments, thermally curing can include a stepwise thermal curingprocess. For example, the step wise thermal curing can include aplurality of steps lasting between about 10 minutes and 6 hours, andwherein the steps have a temperature increase between successive stepsof between about 10 degrees Celsius and 50 degrees Celsius. Inparticular embodiments, the temperature during any and/or all of thesteps can be between about 80 degrees Celsius to no greater than about450 degrees Celsius.

Thermal curing may be conducted such that a desired porosity of firstlayer 30 can be obtained. For example, thermal curing may be conductedsuch that the porosity of first layer 30 is at least about 0.1%.

In certain embodiments, the method may further include depositing anintermediate layer 90 between the substrate and the first layer 30. Forexample, an intermediate layer 90 may be provided to improve adhesionbetween the first layer 30 and the substrate. As can be appreciated byone of skill in the art, the particular choice of intermediate layer 90will depend on the substrate and composition of first layer 30. Inparticular embodiments, the intermediate layer 90 may contain zinc or azinc containing compound.

In certain embodiments, the method may include mechanically treating thesurface of the substrate adjacent first layer 30, to improve adhesionbetween first layer 30 and the substrate. In such embodiments, thesubstrate can directly contact the first layer 30. Mechanically treatingthe surface of the substrate can include, for example, blasting ormechanically etching the surface of the substrate. In fact a particularadvantage of certain embodiments of the present disclosure is anexcellent adhesion between a substrate and the first layer as describedherein, particularly metal substrates such as steel. For example, it wasbelieved that adhesion would be difficult due to the difference inthermal expansion of the first layer and the substrate. However, withoutwishing to be bound by theory, the inventors were able to carefullycontrol the curing conditions and produce a composite with an excellentadhesion between the substrate and the first layer from an in-situ,continuous, composite formation process.

In certain embodiments, the method may further include providing acatalyst and mixing the catalyst with the other components in themixture. In particular embodiments, the catalyst can be first combinedwith the thermoplastic and that combination may be mixed with the othercomponents of the mixture. The catalyst can accelerate the imidizationof the polyamic acid.

In particular embodiments, the catalyst can include a strong tertiaryaliphatic base, such as, for example, 1, 4-diazabicyclo[2.2.2]octane(DABCO); 1, 8-diazabicyclo[5.4.0]undec-7-ene (DBU); a nitrogencontaining base; phenol; or an amphoteric material.

The method may further include providing and blending a desired additiveinto the mixture. For example, some additives may include a thickener orstabilizer.

In certain embodiments, and referring in particular to FIG. 18, thepolyimide layer can be formed and cured separately from the substrate,and then laminated to the substrate with, for example, a laminatingadhesive. For example, as illustrated in FIG. 18, the compositeprecursor 100 can include a first substrate 105, such as a releaselayer, and the cured polyimide based layer 110 disposed adjacent thefirst substrate 105. Following, and referring to FIG. 19, the compositeprecursor 101 can include an adhesive layer 120 disposed adjacent thepolyimide based layer 100, and then a second substrate 130, such as ametallic substrate, and more particularly a steel substrate, is disposedadjacent the adhesive layer 120. The release layer can then be removedfrom the composite such that the polyimide based layer 110 forms anouter major surface of the composite 100 as illustrated in FIG. 20.

In particular embodiments, the release layer can be a film, such as aKapton film. The release layer can be treated, such as ionized with UVlight.

The polyimide precursor solution can then be applied to the releaselayer by, for example, spray coating, dip coating, knife coating, rollcoating, or combinations thereof.

The coated release layer can then be cured to imidize the polyimideprecursor and filler mixture.

An adhesive layer can then be applied to the exposed polyimide layer, orto the substrate, and the cured coated release layer can be laminated tothe substrate. The adhesive layer can include, for example, a modifiedETFE film, and epoxy, or combinations thereof.

In particular embodiments, the adhesive layer can include a film, suchas a modified ETFE film, and be adhered within the composite by, forexample, lamination such as hot pressing.

A particular advantage of certain embodiments of the present disclosureis the formation of a composite that has an essentially crack freepolyimide layer. For example, some processes for forming compositebearings deposit the uncured solution directly on the substrate and cureon the substrate. However, polyimide has a much different coefficient ofthermal expansion that typical metallic substrates, which causes thepolyimide layer to shrink and crack during curing when applied directlyto and cured on a metallic substrate. In contrast, producing a compositematerial by forming and curing the polyimide on a release liner and thenlaminating to the metallic substrate has produced a composite that isessentially free of stress induced microcracks and does not delaminate.

To form a composite bearing from the composite sheet material, the sheetmaterial can be at least partially cut and rolled to form a bearinghaving an inner layer (substrate) and an outer layer (first layer 30).

The present disclosure represents a departure from the state of the art.In particular, it has heretofore been unknown how to form a compositebearing which can provide the performance characteristics, andparticularly the combination of performance characteristics describedherein. For example, the present disclosure illustrates variousbearings, seals, and the like having a crosslinked polyimide matrix withcertain filler materials, such as a thermoplastic or organic filler,dispersed within the polyimide matrix. Such constructions as describedin detail herein have unexpectedly been found to exhibit significantlysuperior coefficient of friction values and wear rates that wereheretofore impossible to achieve.

These and other unexpected and superior characteristics are illustratedin the Examples below, which are exemplary and not limiting, in any way,to the embodiments described herein.

Example 1

A two liter reactor equipped with a mechanical stirrer, a thermocouple,a Dean-Stark adapter, and a reflux condenser was charged with fillerF4PN40 and xylene (425 g). The mixture was stirred at 60 degrees Celsiusat 150 rpm to obtain a uniform dispersion of PTFE in the xylene solvent.Then, oxydianiline (ODA, 70 g, 0.350 mol) and N-methylpyrolidone (NMP,433 g) were added. The solution mixture was stirred (150 rpm) and heatedto 160 C under nitrogen gas to remove residual water as a xyleneazeotrope using the Dean-Stark adapter. The mixture was cooled to 60 Cand pyromellitic dianhydride (PMDA, 76.9 g, 0.353 mol) was added to themixture under reaction conditions to a ratio of 1.0000:1.0085 ODA toPMDA. After addition, the reaction mixture was warmed to about 89degrees Celsius, and became extremely viscous. The increase intemperature confirms the exothermic nature of poly(amic acid) formation.The reaction mixture was stirred and heated at 70 degrees Celsius for 2hours, then the stirring was slowed down to 60 rpm and the solution wascooled down to room temperature. A 15% solution of poly(amic acid) wasthus formed. The solution was stored in a clean and pre-dried glassbottle.

The solution of poly(amic acid) was heated to 60 degrees Celsius, andstirred at 12 rpm. The solution was then casted on an aluminumsubstrate. The coated substrate is the thermally cured at 70 degreesCelsius for 1 hour, 100 degrees Celsius for 1 hour, 120 degrees Celsiusfor 1 hour, 140 degrees Celsius for 1 hour, 160 degrees Celsius forabout 30 minutes and at 250 degrees Celsius overnight in a vacuum ovenunder flow of nitrogen. Then composite sheet was cooled down graduallyover about 6 hours and removed from the oven.

3 samples were prepared and tested for coefficient of friction and wearrate. Sample 1 was formed as described above with a 30 wt. % loading ofPTFE and a coating thickness of about 175 microns. Sample 2 was formedthe same as sample 1, except with a PTFE loading of 50 wt. % and acoating thickness of about 70 microns. Sample 3 was formed the same assample 2, except with a coating thickness of about 285 microns.Comparative samples 4-6, which were obtained from Saint-GobainCorporation were also supplied and tested.

Each sample was tested for coefficient of friction and wear rateaccording to ASTM G-77. A schematic illustration of the testconfiguration is illustrated in FIG. 3. During the test, block-on-ringgeometry was used for determining sliding wear of the plastic materials.A stationary block specimen was pressed with a constant force against arotating ring specimen at 90 degrees to the ring's axis of rotation.Friction between the sliding surfaces of the block and ring results inloss of material from both specimens. Wear is calculated using thevolume loss of the block and weight loss of the ring. The temperature ofeach sample was also measured to illustrate the heat build-up during thetest. The results of the test are provided below and in FIGS. 4-9. FIG.4 illustrates a record of the wear and temperature as a function of timefor Sample 1; and FIG. 5 illustrates a record of the coefficient offriction as a function of time for Sample 1. FIG. 6 illustrates a recordof the wear and temperature as a function of time for Sample 2; and FIG.7 illustrates a record of the coefficient of friction as a function oftime for Sample 2. FIG. 8 illustrates a record of the wear andtemperature as a function of time for Sample 3; and FIG. 9 illustrates arecord of the coefficient of friction as a function of time for Sample3.

Samples 1-3 were also observed under a microscope and evaluated for itsmicrostructure with an SEM. The results are illustrated in FIGS. 10-15,in which FIGS. 10 and 11 illustrate the SEM of Sample 1; FIGS. 12 and 13illustrate the SEM of Sample 2; and FIGS. 14 and 15 illustrate the SEMof Sample 3. The SEM images illustrate inhomogeneous distribution of thePTFE filler in all three samples.

TABLE 1 Wear Volume Coefficient of Temperature Sample (mm³) Friction (°C.) 1 1.3 0.17 46 2 0.3 0.22 46 3 0.3 0.21 46 C4 7.8 0.3 60 C5 4.8 0.1748 C6 2.9 0.16 45

As illustrated by the results in Table 1, samples 1-3 exhibited anunexpected and surprising significant improvement in the combination ofwear volume and coefficient of friction. It has heretofore not beenknown how to create a bearing having the combined superior wear volumeand coefficient of friction illustrated in samples 1-3.

Example 2—Polyamic Acid Salt

Three samples were prepared and tested for coefficient of friction indry and lubricated states and compared to the commercially availableNorglide material available from Saint Gobain Performance Plastics. Thethree samples according to certain embodiments of the present disclosurewere prepared as follows:

ODA was dissolved in the mixture of NMP and xylene. With stiffing, samemolar amount of PMDA was added into ODA solution at 60 degrees Celsius,and a polyamic acid solution was obtained after two hours. The samemolar amount of triethylamine was added slowly into the above polyamicacid solution to form a homogenous viscous polyamic acid salt solution.Certain amount of PTFE suspension were mixed with the above polyamicacid salt solution, and used to form a substrate.

The coefficient of friction (COF) test was performed on a Plint tester,also known as a ball-on-flat sliding test. The test was performed undertwo different conditions: lubricated and dry. For the lubricated test,the sample is in an oil bath at room temperature during the entire test.For the dry test, the ball is directly in contact with the sampleswithout any kind of lubrication beyond that provided by the coatingitself. The three samples according to the embodiments of the disclosurewere differentiated as follows:

-   -   25% PTFE and a coating thickness of about 50 microns, prepared        with the following composition:

Mass (g) % solids DI water 2.3 100 PAA salt 2.0 17 PTFE 0.27 50

-   -   35% PTFE and a coating thickness of about 90 microns, prepared        with the following composition:

Mass (g) % solids DI water 2.3 100 PAA salt 2.0 17 PTFE 0.43 50

-   -   45% PTFE and a coating thickness of about 130 microns prepared        with the following composition:

Mass (g) % solids DI water 2.3 100 PAA salt 2.0 17 (12 um particles)PTFE 0.66 50

The oscillation frequency of the ball was 0.11 Hz, the distancetravelled during a period was 3 cm (round trip), the charge was 25 N andtest duration was 5 minutes. The pressure applied to the coating duringthe test should be 53 MPa to be at the same conditions listed forTest 1. The area of contact between the coating and the ball was about5.10⁻⁵ m², so the pressure (with a 25 N load) was close to 50 MPa.

In the lubricated test, all of the PTFE/PI samples had approximately thesame COF as illustrated in Table 8 below. They are all lower than theCOF of Norglide.

TABLE 8 Results of the Plint test for lubricated conditions Coatingcomposition 25% 35% 45% (in solids %) Norglide PTFE PTFE PTFE COFlubricated 0.022 0.017 0.018 0.018 (+/−10%)

In the dry test, the COF values show more differences and decrease withan increase in the weight percent PTFE in the coating (Table 9). Again,all of the PTFE/PI samples are better than the Norglide material.

TABLE 9 Results of the Plint test for dry conditions Coating composition25% 35% 45% (in solids %) Norglide PTFE PTFE PTFE COF dry 0.028 0.0230.018 0.016 (+/−10%)

Many different aspects and embodiments are possible. Some of thoseaspects and embodiments are described below. After reading thisspecification, skilled artisans will appreciate that those aspects andembodiments are only illustrative and do not limit the scope of thepresent invention. Embodiments may be in accordance with any one or moreof the items as listed below.

Example 3: Lamination

Samples according to certain embodiments of the present disclosure wereprepared by coating the 25% PTFE mixture described in Example 2 onto acorona treated Kapton® release film and cured. The coating had athickness of about 70 to 130 um. The composite was then laminated onto azinc plated steel substrate instead of directly coating onto the steelsubstrate as done in Example 2. In one example, a layer of modified ETFEfilm was used between the steel substrate and the cured composite withthe cured coating layer in direct contact with the modified ETFE film.In another example, a layer of epoxy was used between the steelsubstrate and the cured composite. The bearing samples were then hotpressed to cure the modified ETFE layer or epoxy layer. The COF was thenmeasured in the dry conditions as described above in the Plint test,with the following parameters:

The oscillation frequency of the ball was 5 Hz, the distance travelledduring a period was 3 cm (round trip), the charge was 82 N and testduration was 18 minutes. The pressure applied to the coating during thetest should be 53 MPa to be at the same conditions listed for Test 1.The area of contact between the coating and the ball was about 5.10⁻⁵m², so the pressure (with a 82 N load) was close to 53 MPa.

The results of the dry test of the two samples described above arereported in FIG. 16. As shown, similarly excellent COF values wereobtained for both samples.

The sample containing modified ETFE was then tested against commerciallyavailable norglide material and a JBT sample obtained from Saint-GobainPampus, Germany under the tradename Norglide T. The results are reportedin FIG. 17. As shown, the sample according to certain embodiments of thepresent disclosure significantly outperformed the Norglide sample andessentially matched the JBT sample.

Example 3 above illustrates, at least, that samples can be prepared bycoating onto a release film and cured and then laminated onto asubstrate without suffering from shrinkage due to differences in thethermal expansion between the steel substrate and the coating.Accordingly, a superior and longer lasting bearing can be obtained.

Item 1. A bearing comprising:

-   -   a. a substrate; and    -   b. a layer disposed on the substrate, wherein the layer        comprises        -   i. a polyimide matrix; and        -   ii. a filler dispersed within the polyimide matrix, wherein            the filler comprises a thermoplastic or an organic filler.

Item 2. A bearing comprising:

-   -   a. a substrate; and    -   b. a layer disposed on the substrate, wherein the layer        comprises:        -   i. a polyimide matrix derived from a polyamic acid salt; and        -   ii. a thermoplastic and/or organic filler dispersed within            the polyimide matrix.

Item 3. A bearing comprising:

-   -   a. a substrate; and    -   b. a first layer disposed on the substrate, wherein the first        layer comprises a polyimide matrix and a filler dispersed within        the polyimide matrix;    -   c. wherein the bearing has a coefficient of friction of less        than about 1, and a wear resistance of less than about 2.9 mm³.

Item 4. A bearing having a coefficient of friction of less than about 1,and a wear resistance of less than 2.9 mm³.

Item 5. The bearing of any one of items 1-3, wherein the substratecomprises a metal.

Item 6. The bearing of item 4, wherein the metal comprises steel,aluminum, bronze, or copper.

Item 7. The bearing of any one of items 1-3, wherein the bearing has anaverage coefficient of friction (COF) of no greater than about 1, nogreater than about 0.8, no greater than about 0.7, no greater than about0.6, no greater than about 0.5, no greater than about 0.4, no greaterthan about 0.3, no greater than about 0.25, no greater than about 0.2,no greater than about 0.18, no greater than about 0.15, or even nogreater than about 0.12 as measured according to ASTM G-77.

Item 8. The bearing of any one of items 1-3, wherein the bearing has anaverage coefficient of friction (COF) of no less than about 0.001, noless than about 0.01, or even no less than about 0.05 as measuredaccording to ASTM G-77.

Item 9. The bearing of any one of items 1-3, wherein the bearing has awear resistance of no greater than about 10 mm³, no greater than about8mm³, no greater than 5 mm³, no greater than about 4 mm³, no greaterthan about 3 mm³, no greater than about 2.9 mm³, no greater than about 2mm³, no greater than about 1.5 mm³, no greater than about 1.3 mm³, nogreater than about 1.1 mm³, no greater than about 1 mm³, no greater thanabout 0.8 mm³, no greater than about 0.6 mm³, no greater than about 0.5mm³, no greater than about 0.3 mm³, or even no greater than about 0.2mm³ as measured according to ASTM G-77.

Item 10. The bearing of any one of items 1-3, wherein the bearing has awear resistance of no less than about 0.001 mm³, no less than about 0.01mm³, or even no less than about 0.05 mm³ as measured according to ASTMG-77.

Item 11. The bearing of any one of items 1-3, wherein the layer disposedon the substrate passes the Laminator Adhesion Test (Erichsen).

Item 12. The bearing of any one of items 1-3, wherein the layer disposedon the substrate has a thickness of no greater than about 1 mm, nogreater than about 800 microns, no greater than about 500 microns, nogreater than about 300 microns, no greater than about 250 microns, nogreater than about 200 microns, or even no greater than about 175microns.

Item 13. The bearing of any one of items 1-3, wherein the layer disposedon the substrate has a thickness of at least about 0.01 microns, atleast about 1 micron, at least about 50 microns, or even at least about100 microns.

Item 14. The bearing of any one of items 1-3, wherein the layer disposedon the substrate has a porosity of at least about 0.01%, at least about0.05%, or even at least about 0.1%.

Item 15. The bearing of any one of items 1-3, wherein the polyimidematrix comprises a crosslinked and imidized polyamic acid.

Item 16. The bearing of item 14, wherein the polyamic acid or polyamicacid salt comprises a reaction product of two different monomersselected from the group consisting of: pyromellitic dianhydride (PMDA),3,3′-4, 4′-biphenyltetracarboxylic dianhydride (BPDA), 2, 2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA), 2, 2′-bis[4-(3, 4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA),benzophenonetetracarboxylic dianhydride (BTDA), and 4, 4′-oxydianiline(ODA), or m-phenylene diamine (m-PDA), 4, 4′-diaminophenyl sulphone(4,4′-DDS), p-phenylene diamine (p-PDA), and methylene dianiline (MDA).

Item 17. The bearing of item 14, wherein the polyamic acid or polyamicacid salt comprises a reaction product of a first monomer and a secondmonomer, wherein the first and second monomers are different.

Item 18. The bearing of item 16, wherein the first monomer comprises amonomer selected from the group consisting of pyromellitic dianhydride(PMDA), 3,3′-4, 4′-biphenyltetracarboxylic dianhydride (BPDA), 2, 2-bis(3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA), 2, 2′-bis[4-(3, 4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA),benzophenonetetracarboxylic dianhydride (BTDA), and any combinationthereof; and wherein the second monomer comprises a monomer selectedfrom the group consisting of 4, 4′-oxydianiline (ODA), or m-phenylenediamine (m-PDA), 4, 4′-diaminophenyl sulphone (4,4′-DDS), p-phenylenediamine (p-PDA), methylene dianiline (MDA), and any combination thereof.

Item 19. The bearing of any one of the preceding items, wherein thepolyimide matrix is derived from a polyamic acid salt.

Item 20. The bearing of any one of the preceding items, wherein thepolyimide matrix comprises an imidized reaction product of a polyamicacid salt.

Item 21. The bearing of any one of items 1-3, wherein the thermoplasticcomprises a fluoropolymer.

Item 22. The bearing of item 18, wherein the thermoplastic comprises aperfluoropolymer.

Item 23. The bearing of item 18, wherein the thermoplastic comprisesPTFE.

Item 24. The bearing of item 20, wherein the thermoplastic comprisesPTFE regrind.

Item 25. The bearing of any one of items 1-3, wherein the thermoplasticis present in the layer in an amount of from greater than 0 to 80% byweight, based on the combined weight of the thermoplastic and thepolyimide matrix.

Item 26. The bearing of any one of items 1-3, wherein the polyimidematrix is present in the layer in an amount of from 20 to 100% byweight, based on the combined weight of the thermoplastic and thepolyimide matrix.

Item 27. The bearing of any one of items 1-3, wherein the layer disposedon the substrate further comprises an organic filler.

Item 28. The bearing of item 24, wherein the organic filler is presentin the layer in an amount of from greater than 0% to 80% by weight,based on the combined weight of the thermoplastic, polyimide matrix, andorganic filler.

Item 29. The bearing of any one of items 1-3, wherein the bearingfurther comprises an intermediate layer disposed between the substrateand the layer.

Item 30. The bearing of item 26, wherein the intermediate layercomprises zinc or a zinc containing compound.

Item 31. A method of forming a composite bearing comprising:

-   -   a. providing a polyimide precursor or imide monomers;    -   b. providing a thermoplastic;    -   c. blending the thermoplastic, the polyimide precursor or imide        monomers, and a solvent to form a mixture;    -   d. depositing the mixture on a substrate;    -   e. thermally curing the substrate and deposited mixture to        thereby imidize the polyimide precursor and form a composite        sheet.

Item 32. A method of forming a composite bearing, the method comprising:

-   -   a. providing a polyimide precursor or imide monomers;    -   b. providing an organic filler;    -   c. blending the filler, the polyimide precursor or imide        monomers, and a solvent to form a mixture;    -   d. depositing the mixture on a substrate;    -   e. thermally curing the substrate and deposited mixture to        thereby imidize the polyimide precursor and form a composite        sheet.    -   f. forming a bearing from the composite sheet.

Item 33. A method of forming a composite bearing, the method comprising:

-   -   a. providing a polyimide precursor or imide monomers;    -   b. providing an organic filler and/or a thermoplastic;    -   c. blending the organic filler and/or thermoplastic, the        polyimide precursor or imide monomers, and a solvent to form a        mixture;    -   d. depositing the mixture on a substrate;    -   e. thermally curing the substrate and deposited mixture to        thereby imidize the polyimide precursor and form a composite        sheet; and    -   f. forming a bearing from the composite sheet;    -   g. wherein the bearing has a coefficient of friction of less        than about 1, and a wear resistance of less than 2.9 mm³

Item 34. The method of any one of items 28-30, wherein thermally curingcomprises a stepwise thermal curing.

Item 35. The method of item 31, wherein the stepwise thermal curingincludes a plurality of steps, wherein each step lasts between about 10minutes and 6 hours, and wherein each step has a temperature increasebetween successive steps of between about 10 degrees Celsius and 50degrees Celsius.

Item 36. The method of any one of items 28-30, wherein the solventcomprises N-methyl-pyrrolidone (NMP), dimethylformamide,dimethylacetamide, diglyme, dimethylsulfoxide, xylene, or anycombination thereof.

Item 37. The method of any one of items 28-30, wherein the polyimideprecursor comprises polyamic acid.

Item 38. The method of any one of the preceding items, wherein thepolyimide precursor comprises polyamic acid salt.

Item 39. The method of item 34, wherein the polyamic acid or polyamicacid salt is derived from at least two different monomers selected fromthe group consisting of: pyromellitic dianhydride (PMDA), 3,3′-4,4′-biphenyltetracarboxylic dianhydride (BPDA), 2, 2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA), 2, 2′-bis[4-(3, 4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA),benzophenonetetracarboxylic dianhydride (BTDA), and 4, 4′-oxydianiline(ODA), or m-phenylene diamine (m-PDA), 4, 4′-diaminophenyl sulphone(4,4′-DDS), p-phenylene diamine (p-PDA), and methylene dianiline (MDA).

Item 40. The method of item 34, wherein the polyamic acid or polyamicacid salt is derived from a first monomer and a second monomer, andwherein the first and second monomer are different.

Item 41. The method of item 36, wherein the first monomer comprises amonomer selected from the group consisting of pyromellitic dianhydride(PMDA), 3,3′-4, 4′-biphenyltetracarboxylic dianhydride (BPDA), 2, 2-bis(3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA), 2, 2′-bis[4-(3, 4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA),benzophenonetetracarboxylic dianhydride (BTDA), and any combinationthereof; and wherein the second monomer comprises a monomer selectedfrom the group consisting of 4, 4′-oxydianiline (ODA), or m-phenylenediamine (m-PDA), 4, 4′-diaminophenyl sulphone (4,4′-DDS), p-phenylenediamine (p-PDA), methylene dianiline (MDA), and any combination thereof.

Item 42. The method of any one of items 28-30, wherein the thermoplasticcomprises a fluoropolymer.

Item 43. The method of any one of items 28-30, wherein the thermoplasticcomprises a perfluoroplymer.

Item 44. The method of any one of items 28-30, wherein the thermoplasticcomprises PTFE.

Item 45. The method of any one of items 28-30, wherein the thermoplasticcomprises PTFE regrind.

Item 46. The method of any one of items 28-30, wherein the thermoplastichas an average particle size (D₅₀) of at least 1 about 1 micron, atleast about 3 microns, at least about 5 microns, at least about 10microns, at least about 15 microns, or even at least about 20 microns.

Item 47. The method of any one of items 28-30, wherein the thermoplastichas an average particle size (D₅₀) of no greater than about 50 microns,no greater than about 30 microns, no greater than about 20 microns, oreven no greater than about 10 microns.

Item 48. The method of any one of items 28-30, wherein the thermoplastichas an average particle size (D₅₀) with a range of between about 1micron and 50 microns, about 3 microns to about 30 microns, or evenabout 5 microns to about 20 microns.

Item 49. The method of any one of items 28-30, wherein the thermoplasticis in a powdered form.

Item 50. The method of any one of items 28-30, wherein the thermoplasticis in a dispersed phase.

Item 51. The method of any one of items 28-30, wherein the thermoplastichas an average particle size of at least 0.05 microns, at least about0.1 micron, or even at least about 2 microns.

Item 52. The method of any one of items 28-30, wherein the thermoplastichas an average particle size of no greater than about 1000 microns, nogreater than about 500 microns, or even no greater than about 100microns.

Item 53. The method of any one of items 28-30, wherein the viscosity ofthe mixture is adjusted to form a predetermined thickness of the mixturedeposited on the substrate.

Item 54. The method of any one of items 28-30, wherein the thermoplasticis present in the mixture in an amount of from greater than 0 to 80% byweight, based on the combined weight of the thermoplastic and thepolyimide precursor.

Item 55. The method of any one of items 28-30, wherein the polyimideprecursor is present in the mixture in an amount of from 20 to 100% byweight, based on the combined weight of the thermoplastic and thepolyimide precursor.

Item 56. The method of any one of items 28-30, further comprisingproviding an organic filler, and mixing the organic filler with thethermoplastic.

Item 57. The method of item 52, wherein the organic filler is present inthe mixture in an amount of from greater than 0% to 80% by weight, basedon the combined weight of the thermoplastic, polyimide precursor, andorganic filler.

Item 58. The method of any one of items 28-30, wherein the substratecomprises a metal.

Item 59. The method of item 54, wherein the metal comprises steel,aluminum, bronze, copper, or combinations thereof.

Item 60. The method of any one of items 28-30, further comprisingtreating the substrate to improve adhesion between the deposited mixtureand the substrate prior to deposition of the mixture on the substrate.

Item 61. The method of item 56, wherein treating comprises chemicallytreating a surface of the substrate adjacent the layer prior todeposition of the mixture on the substrate.

Item 62. The method of item 57, wherein chemically treating comprisescoating the surface of the substrate with a composition comprising zincor a zinc containing compound.

Item 63. The method of item 56, wherein treating comprises mechanicallytreating a surface of the substrate adjacent the layer prior todeposition of the mixture on the substrate.

Item 64. The method of item 59, wherein mechanically treating comprisessand blasting or mechanically etching the surface of the substrate.

Item 65. The method of any one of items 28-30, further comprisingforming more than one layer comprising a polyimide matrix on thesubstrate.

Item 66. The method of any one of items 28-30, further comprising addinga second filler to the mixture.

Item 67. The method of item 62, wherein the second filler is selectedfrom the group consisting of carbon graphite, grapheme, carbonnanotubes, ekonol, glass fibers, a polymeric compound, an inorganiccompound, and combinations thereof.

Item 68. The method of any one of items 28-30, wherein thermally curingcomprises controlling the temperature such that the composite has aporosity of at least about 0.1%.

Item 69. The method of any one of items 28-30, further comprisingproviding a catalyst and mixing the catalyst with the thermoplastic.

Item 70. The method of item 65, wherein the catalyst acceleratesimidization of the polyamic acid.

Item 71. The method of item 65, wherein the catalyst comprises a strongtertiary aliphatic base.

Item 72. The method of item 65, wherein the catalyst comprises 1,4-diazabicyclo[2.2.2]octane (DABCO); 1, 8-diazabicyclo[5.4.0]undec-7-ene(DBU); a nitrogen containing base; phenol; or an amphoteric material.

Item 73. The method of any one of items 28-30, wherein the method is acontinuous process.

Item 74. The method of any one of items 28-30, further comprising atleast partially cutting the coated substrate.

Item 75. The bearing or method of any one of the preceding items,wherein the filler comprises an aromatic polyester, a recycledpolyimide, polyamide ether imide, polyamide imide, PEEK, PEEK-likepolymers of polyaryl family, liquid crystalline polymers (LCP),polybenzimidazole, or combinations thereof.

Item 76. The bearing or method of any one of the preceding items,wherein the organic filler comprises an aromatic polyester, a recycledpolyimide, polyamide ether imide, polyamide imide, PEEK, PEEK-likepolymers of polyaryl family, liquid crystalline polymers (LCP),polybenzimidazole, or combinations thereof.

Item 77. The method of any one of the preceding items, wherein thesubstrate is a release film, and wherein the method further comprisingcuring the mixture on the release film, and after, forming a compositewith a steel substrate.

Item 78. The method of item 77, wherein the method further comprisesremoving the release film after formation of the composite with a secondsubstrate such that the cured mixture forms an outer surface of thebearing.

Item 79. The method of item 78, wherein the second substrate comprises ametallic substrate.

Item 80. The method of item 79, wherein the second substrate comprisessteel.

Item 81. The method of any one of the preceding items, wherein therelease film is surface treated before deposition of the mixture.

Item 82. The method of any one of the preceding items, wherein thesecond substrate is a zinc coated steel substrate.

Note that not all of the activities described above in the generaldescription or the examples are required, that a portion of a specificactivity may not be required, and that one or more further activitiesmay be performed in addition to those described. Still further, theorder in which activities are listed is not necessarily the order inwhich they are performed.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any feature(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature of any or all the claims.

The specification and illustrations of the embodiments described hereinare intended to provide a general understanding of the structure of thevarious embodiments. The specification and illustrations are notintended to serve as an exhaustive and comprehensive description of allof the elements and features of apparatus and systems that use thestructures or methods described herein. Separate embodiments may also beprovided in combination in a single embodiment, and conversely, variousfeatures that are, for brevity, described in the context of a singleembodiment, may also be provided separately or in any subcombination.Further, reference to values stated in ranges includes each and everyvalue within that range. Many other embodiments may be apparent toskilled artisans only after reading this specification. Otherembodiments may be used and derived from the disclosure, such that astructural substitution, logical substitution, or another change may bemade without departing from the scope of the disclosure. Accordingly,the disclosure is to be regarded as illustrative rather thanrestrictive.

What is claimed is:
 1. A bearing comprising: a. a substrate; and b. a first layer disposed on the substrate, wherein the layer comprises i. a polyimide matrix; and ii. a filler dispersed within the polyimide matrix, wherein the filler comprises a thermoplastic and/or an organic filler.
 2. The bearing of claim 1, wherein the substrate comprises a metal substrate.
 3. The bearing of claim 1, wherein the substrate steel, aluminum, bronze, or copper.
 4. The bearing of claim 1, wherein the polyimide matrix comprises a crosslinked and imidized polyamic acid or polyamic acid salt.
 5. The bearing of claim 4, wherein the crosslinked and imidized polyamic acid or polyamic acid salt comprises a reaction product of two different monomers selected from the group consisting of: pyromellitic dianhydride (PMDA), 3,3′-4, 4′-biphenyltetracarboxylic dianhydride (BPDA), 2, 2-bis (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA), 2, 2′-bis [4-(3, 4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA), benzophenonetetracarboxylic dianhydride (BTDA), and 4, 4′-oxydianiline (ODA), or m-phenylene diamine (m-PDA), 4, 4′-diaminophenyl sulphone (4,4′-DDS), p-phenylene diamine (p-PDA), and methylene dianiline (MDA).
 6. The bearing of claim 1, wherein the filler comprises a thermoplastic fluoropolymer.
 7. The bearing of claim 1, wherein the filler comprises a thermoplastic perfluoropolymer.
 8. The bearing of claim 1, wherein the filler comprises PTFE.
 9. The bearing of claim 1, wherein the filler comprises an organic filler.
 10. The bearing of claim 1, wherein the filler comprises a thermoplastic filler and an organic filler.
 11. The bearing of claim 1, wherein the filler is present in the first layer in an amount of from greater than 0 to 80% by weight, based on the combined weight of the filler and the polyimide matrix.
 12. The bearing of claim 1, wherein the bearing has a coefficient of friction of less than about 1, and a wear resistance of less than about 2.9 mm³.
 13. The bearing of claim 1, a. wherein the substrate comprises steel; b. wherein the polyimide matrix comprises a crosslinked and imidized polyamic acid or polyamic acid salt; c. wherein the filler comprises PTFE; and d. wherein the bearing has a coefficient of friction of less than about 1, and a wear resistance of less than about 2.9 mm³.
 14. A bearing comprising: a. a metal substrate; and b. a first layer, wherein the first layer comprises a polyimide matrix and a filler dispersed within the polyimide matrix; c. wherein the bearing has a coefficient of friction of less than about 1, and a wear resistance of less than about 2.9 mm³.
 15. The bearing of claim 14, wherein the bearing further comprises an adhesive layer disposed between the metal substrate and the first layer.
 16. A method of forming a bearing, the method comprising: a. providing a first substrate; b. depositing a mixture comprising a polyimide precursor or imide monomers and a thermoplastic filler and/or organic filler onto the first substrate; c. curing the mixture to thereby imidize the polyimide precursor or imide monomers.
 17. The method of claim 16, wherein the first substrate comprises a metal substrate.
 18. The method of claim 16, further comprising; a. providing a second substrate; b. disposing an adhesive layer between the second substrate and the cured mixture; c. curing the adhesive layer to form a bearing.
 19. The method of claim 18, wherein the first substrate comprises a release layer and the second substrate comprises a metal substrate.
 20. The method of claim 19, wherein the method further comprises removing the release layer such that the cured mixture forms an outer major surface of the bearing. 